412 HANDBOOK OF PROTOZOOLOGY 



In order to collect parasitic forms, one must, of course, find 

 the host animals that harbor them. Various species of frogs, 

 tadpoles, cockroaches, etc., which are of common occurrence or 

 easily obtained and which are hosts to numerous species of 

 Protozoa, are useful material for class work. In the case of in- 

 testinal Protozoa of vertebrates, freshly voided fecal matter 

 should be collected in a clean and dry container, and micro- 

 scopical examination should be made immediately. 



Cultivation 



For extensive study or for class work, large numbers of a 

 certain species of Protozoa are frequently desirable, and this 

 makes it necessary to provide favorable conditions for their 

 growth and multiplication. Success in culturing Protozoa de- 

 pends upon several factors. First, an abundant supply of proper 

 food material is needed to enable the organisms to grow and 

 multiply more rapidly than under natural conditions. For 

 example, several species of Paramecium live almost exclusively 

 on bacilli, while Coleps, Didinium, and allied forms depend on 

 other ciliates as sources of food supply. For cultivating the 

 Phytomastigina successfully, good light and a fairly large 

 amount of inorganic substances are necessary. In the second 

 place, the temperature and chemical constituents of the medium 

 seem to have a far greater influence on the multiplication of 

 protozoans than was thought heretofore. As a rule, a lower 

 temperature seems to be much more favorable for culture than a 

 higher one, although this is not the case with the parasitic forms 

 occurring in warm-blooded animals. Recent investigations show 

 also the importance of a proper hydrogen ion concentration. 

 In the third place, both protozoans and metazoans which prey 

 upon the forms under cultivation must be excluded from the 

 culture. For instance, it is necessary to remove Didinium 

 nasiitum in order to obtain a rich culture of Paramecium. 



Mixed cultures of several free-living forms are compara- 

 tively easily maintained by adding a small amount of cut-up 

 hay to the water, although the protozoan population changes a 

 great deal from time to time. Amoeba, Vahlkampfia, Arcella, 

 Peranema, Bodo, Paramecium, Stylonychia, and many other 

 forms often multiply abundantly in such cultures. To obtain 



